1. Field of the Invention
From German Patent DE 101 33 218 C2, a method and an apparatus for adjusting the magnet stroke in fuel injectors is known. According to DE 101 33 218 C2, the installation of a solenoid valve, in which an electromagnet is surrounded by a magnet sleeve is fixed in an opening in an injector body, is effected in that the magnet sleeve is received on the injector body by means of a magnet adapter nut, and an adjusting disk is disposed between the end face of the magnet sleeve and the injector body. First, a preadjustment of the stroke of an armature is made by means of an adjusting disk; a preselectable attraction torque is exerted on the magnet adapter nut upon tightening onto the injector cap, and elastic elements are embodied in the screw assembly that comprises the injector cap and the magnet adapter nut. During the tightening of the magnet adapter nut, the stroke travel of the armature is absorbed.
2. Description of the Prior Art
In installation methods currently used, the magnet adapter nut is screwed on with a constant rotational speed, while at the same time, the stroke and the closing duration of the solenoid valve are measured. The time that elapses from when the coil current is shut off until the valve element strikes the sealing seat is calculated as the closing duration. Measuring the closing duration partly replaces measuring the valve stroke, since the valve stroke, in certain types of injector, can no longer be measured in the installed state. It is then necessary that the change in the stroke or closing duration of the solenoid valve be virtually constant over time, at a constant rotational speed of the magnet adapter nut, so that the screwing device detects the attainment of the target stroke in good time and terminates the screwing operation. This condition is largely met, if the deformation is a purely elastic deformation. However, there is also the additional condition that the torque exerted be between a minimum value and a maximum value. The minimum value is defined by the fact that independent loosening at overly low breakaway torques must be prevented. The maximum value, on the other hand, is defined by the fact that the components ensure their resistance to failure only up to a certain torque. Because of this restriction, there is only a certain range within which the valve stroke can be finely adjusted. This range can be further restricted if the plastic deformation of the magnet sleeve occurs at lesser torques than Mmax, and in that case the constant change in the stroke over time is no longer given.
The usable adjustment travel of the valve stroke, which is described by the above conditions, is not sufficiently long to make it possible to compensate for an error in the selection of the adjusting disk and variations in the rigidity of the magnet sleeve and in the moments of friction between the magnet adapter nut and the injector body or magnet sleeve. This in turn means that some fuel injectors cannot be adjusted to the target stroke and have to be removed. In particular, the range of the onset of plastic deformation in injectors at this time is at torques below the upper torque limit, which is defined by the strength of the other components. Designing the magnet sleeve for lesser rigidities and thus a wider adjustment range within the torque limits Mmin and Mmax leads in turn to a plastic deformation that begins even earlier.